Messages in this thread | | | Date | Tue, 01 Jun 2010 14:52:42 +0200 | From | Lukasz Gromanowski <> | Subject | Re: constant half-byte from /proc/sys/kernel/random/uuid |
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Petr Ovtchenkov pisze: > Lack of randomness during generating uuid. > > Sample: > > for i in 1 2 3 4 5 6 7 8 9; do cat /proc/sys/kernel/random/uuid ; done > > 3faf5c7e-5e1b-4b3c-a318-979653d85404 > a929d2d3-e229-42ca-9f33-9c09801f41fb > c2a96cb6-0dba-401c-a9c6-dabe1dec89d6 > df341de3-eb97-4327-bb63-46afd8dbfaa8 > 9d84d61c-0c55-4914-8bd6-7f1601110908 > 6d82e69b-418e-4189-b5a4-0661b6e24dcf > eb38de66-4e0b-4bd0-827b-e75ba273e85a > 5585c367-754f-4bbf-81f6-8a728380860d > c074480b-ad5c-4e10-81d2-82225c449b91 > > > See on 7th high half-byte: it '4' in > all cases---4b, 42, 40, 43, 49, 41, > 4b, 4b, 4e. Checked three comps, with > similar results. All Linux-generated UUID (boot_id) > that I see in internet has '4' in this > half-byte.
Hi, quote from wikipedia[1]
"Version 4 (random)
Version 4 UUIDs use a scheme relying only on random numbers. This algorithm sets the version number as well as two reserved bits. All other bits are set using a random or pseudorandom data source. Version 4 UUIDs have the form xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx with any hexadecimal digits for x but only one of 8, 9, A, or B for y. e.g. f47ac10b-58cc-4372-a567-0e02b2c3d479."
[1] http://en.wikipedia.org/wiki/Universally_Unique_Identifier
-- best regards, Lukasz
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